If $x \triangleleft y = (4-x)(y)$ and $x \circledcirc y = 2x-7y$, find $5 \triangleleft (0 \circledcirc 1)$.
Answer: First, find $0 \circledcirc 1$ $ 0 \circledcirc 1 = (2)(0)-(7)(1)$ $ \hphantom{0 \circledcirc 1} = -7$ Now, find $5 \triangleleft -7$ $ 5 \triangleleft -7 = (4-5)(-7)$ $ \hphantom{5 \triangleleft -7} = 7$.